Both the DKO and TKO mice present with autoimmune-like features including splenomegaly, lymphadenopathy, and the presence of an autoinflammatory B220+ CD3+ cell population which accumulates with age, reminiscent of Fas/FasL deficient mice, which likely contributes to the Autoimmune Lymphoproliferative Syndrome (ALPS) in these mice (7, 8). The gene discussed is FAS; the disease is autoimmune lymphoproliferative syndrome.